Field of Invention
The present invention relates to a power converter circuit for controlling an output current according to information of a primary side voltage of a transformer, wherein the information of the primary side voltage is obtained by sensing a secondary side voltage of the transformer. The present invention also relates to a power limit control circuit for use in the power converter circuit.
Description of Related Art
Please refer to FIG. 1A, an AC input voltage is rectified by a rectification circuit such as a bridge rectifier, to generate a rectified voltage. An input capacitor is connected to the output of the rectification circuit, for filtering the rectified voltage to generate a filtered voltage. A power converter circuit converts the filtered voltage to a DC output voltage. Because the AC input voltage may be unstable, which may affect the quality of the DC output voltage, the input capacitor is provided to reduce the ripple of the rectified voltage.
Referring to FIGS. 1A and 1B, the rectified voltage which is not filtered is a semi-sinusoidal wave having a lower valley, while the filtered voltage is a semi-sinusoidal wave having a higher valley, so the ripple of the filtered voltage is smoother. (The waveform of filtered voltage is not a “pure” semi-sinusoidal wave, but is still regarded as a semi-sinusoidal wave in the context of this invention. That is, any waveform that includes at least a part of a pure semi-sinusoidal waveform is regarded as a semi-sinusoidal waveform in the context of this invention.) However, in order to achieve this effect, a capacitor of a high capacitance is required for the input capacitor, which is expensive and occupies a large space. Further, when the capacitor is aged, it may not be able to provide a good ripple-filtering effect. Therefore, a flexible, space-saving and cost effective solution to reduce the ripple is desired.